Protein-ligand interactions studied by NMR

Various solution NMR experiments for studying protein-ligand interactions have become indispensable techniques in both academia and industry. In general, solution NMR is superior to other physico-chemical methods, in terms of its spatial resolution and the fact that protein modifications are not required. The applications are loosely classified into two categories, "ligand-based approach" and "protein-based approach." Many unique experiments have been developed for the ligand-based approach, including STD, WaterLOGSY, DIRECTION, INPHARMA, ILOE, and trNOE. These experiments frequently comprise the important steps of a drug-discovery process, including ligand screening, pharmacophore mapping, and molecular design. This review provides a practicable classification of these experiments, to promote the selection of a suitable experiment depending on the purpose. In contrast, the variation of experiments in the protein-based approach is rather limited. The ¹H-¹⁵N-HSQC-based NMR titration experiment and its variants are preferentially used for analyses of protein-ligand interactions. This review also discusses several practical aspects of the NMR titration experiment, including sample handling and data acquisition and analysis.